pallet macro: allow to declare individual unbounded storage for those who cannot go into PoV

[gui1117]

This PR introduce a new attribute in the pallet macro for storage: pallet::unbounded.

This attribute allow to declare that a storage doesn't have bounds on its keys and value types and thus only generate partial storage information.

For storage who cannot go into PoV this is useful. Like system event for instance.

Limitation: Maybe the some storage might want to express the bounds on the key types but not the bound on the value. Currently the storage info doesn't support this. I think we can implement more fine grained description when the need comes.

[kianenigma]

LGTM, why is the system::event not already tagged?

[gui1117]

for now event goes into PoV, and frame_system doesn't declare the storage info bounds, so no storage are bounded.

[emostov]

This seems like a change in api: before we errored if there was more than 1 getter or name. Now we simply skip anything after the first one.

for example we had

		if names.len() > 1 {
			let msg = "Invalid pallet::storage, multiple argument pallet::storage_prefix found";
			return Err(syn::Error::new(names[1].attr_span(), msg))
		}

[emostov]

looking at the UI tests though it seems like it still complains about a duplicate attribute, is this just now an error we can rely on the compiler for?

[gui1117]

the duplicate attribute is not from the compiler it is from the last matching arm below, in case rename_as is already some, then the last matching are is branched and the error is raised

[emostov]

My understanding of the proc-macro libs is really not great, but from my level of understanding it looks ok.

[gui1117]

bot merge

[ghost]

Waiting for commit status.